I've always though that the Falcon's flight trajectory was preset. After all, the technicians messed up its hyper-drive, maybe it was programmed to fly towards the Executor? Yes, it does have the plot-hole that they went to get Luke first, but still..
Also, I'm not sure how it is explained in the EU, but can a ship's tractor beam hold on to another ship, if the latter engages its hyper-drive engine? Maybe Lando and Chewie didn't care about the tractor beams (and thus flying towards the Executor), as long as they got the hyper-drive working.
Star Wars space physics is a strange thing, and a Star Destroyer is apparantly a very fast thing, able to keep up with the Falcon during the chase through open space. I figure they spotted the SSD, tried to fly away, but due to this unseen speed that is made to seem slow because of how massive the ships are, the Executor can still intercept the Falcon without it's modified hyperdrive. In ANH Han also boasts that he can outrun the "big corellian ships", which is apparantly a speed benchmark. Would make sense again that he empire posesses the best equipment.
And also in ANH the incoming star destroyer quickly catches up with the falcon, revelaing that the only arena in which the falcon can actually outrun them is hyperspace. "I thought you said his thing was fast?!"